Water flooding of oil fields



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Patented Feb. 10, 1942 WATER FLOODING OF OIL FIELDS Harvey T. Kennedy,Forest Hills, Pa., assignorto Gulf Research & Development Company,Pittsburgh, Pa... a corporation of. Delaware.

No'Drawing. Application MarchZS, 1936,

' Serial No. 70,542 e 6 Claims.

This invention relates to water flooding of oil fields; and it comprisesan ii'rl'phdted process of oil production by water flooding of oil wellstrata of diflering porosities or permeabilities wherein expulsion ofoil by water flooding results from displacement of oil contained in theporous strata, each stratum acting as a unit and inde pendently of allother strata. In the early floodsuitable material adapted toimpregnatethe pores ing. of a pool, the oil is ejected from the'more ofthe strata is injected through one or more inpermeable strata first,leaving the less permeable put wells into the strata in quantitysufficient to strata still largely saturated with oil except in diminishin a desired degree the permeability of zones near the input wellthrough which the the strata and. thus to reduce or prevent by-pass-Water is introduced. Subsequently, the volume ing of water to productionwells and the water 10 of water which by-passes the oil, that is, whichflooding is then continued, advantageously at inflows from the inputwell to the production well creased pressure; the impregnating materialswithout expelling appreciable volumes of oil, is used beingadvantageously solutions of certain large because it is flowing throughthe looser or metallic salts and these solutions being so inmoreporousstrata and also because the viscosity jected' as to formprecipitates in the pores of the of water is considerably lower thanthat of most strata; allas more fully hereinafter set forth and oils. Asthe water flood breaks through the varias claimed. ous strata in theorder of their decreasing per- The deliberate water flooding of anoilfield for meability, the water-oil ratio increases and finalthepurpose of reviving the production of oil 3' reaches a point Whereflooding can no lon therefrom after depletion was first practiced in becontinued profitably by present methods. the Bradford field; the resultsof water flooding I have found that in an oil bearing formation being aseveral fold increase in the rate of probeing fl With y-p ng 0f t e W ers duction of the wells in the flooded region and in described, whenthere is injected into the formathe total production. However, waterflooding tion together with the'water a substance which has not as yetcome into general use because of acts to p the pores of the S t bstancedifficulties encountered in the by-passing or is distributed between thestrata delivering water channeling of water, resulting in the flow ofand those delivering oil in about the same ratio, many'volumes ofW-aterinto the production wells Substantially, as the W ratio, e greater foreach volume of oil produced. part of the impregnating material findingits 1 In the present invention, the di'fficulty due to way to the, Watercarrying Stra Upo j by-passing of Water is minimized. I have found tionof the p p qu y of n obstructing it possible to effect a differentialreduction of a nt, t av effective decrease in p rpermeability in strataof differing porosities by meab i y is greater in the stratacarryingater injecting into the strata material's impregnating than in e Stratadelivering 0i1int0 h p d ctheir pores. While it might appear that theint o W water-Oil ratio being p opo o a ejection into the oil bearingstrata of a material 3 decreased- The advantage of the p v d whichobstructs the flow of liquid through th method of water flooding residesin this difierstrata would lower the efliciency or the water ential orpreferential reduction of porosity due flooding process by increasingthe pressure re- 40 in considerable measure to the fact that as theuired, I ha found howe th t th t effect viscosity of the oil produced isgreater than that of injecting obstructing materials into the strata fthe Water introduced e rate of flow of the is usually to increase theefiiciency by decreasing mp a ng material into the oil producing theamount of water that must be pumped for a Strata is further r givenquantity of oil expelled; increase of pres- If, for example, theviscosity of the oil expelled sure raising the rate of oil' expulsion.The profrom a given stratum happens to be ten times duction of oil isincreased. and the quantity of the viscosity of the water whichdisplaces it, the water pumped may be decreased. pressure drop from theinput well to the junction Underground oil reservoirs almost alwaysconbetween the oil and water, for steady flow, will sist of layers ofsand of Widely diflering perbe one-tenth of that between this junctionand mea y alternating With layers of Shale the production well, assumingthat the input other impermeable rock. These shale breaks? well isreceiving only water and the production or p sf d er in lateral e e TheyeX- well is receiving only oil from the stratum under tend over areasoften as small as a few acres and consideration. Because of the factthat the pores sometimes as large as several square miles. The 5.5

of the: oil bearing: stratum can receive impregnating material carriedby the water only in the sections where it is occupied by water andwhere, due to the comparatively low viscosity of water, the resistanceto flow is small, it follows that the flow through the stratumdelivering oil is but slightly diminished by impregnation. In the caseof the stratum which carries only water from the input well to theproduction well, however, the flow is strictly proportional to thepermeability. If by impregnation of the pores of this stratum itsaverage effective permeability is cut down, say 80 per cent, the flow ofwater is cut down 80 per cent. And if now the water pressure maintainedupon the input Well is increased so that the same amount of water istaken into the reservoir as before, the flow of oil may be increased,roughly, five-fold.Actually, as I have found, since the oil bearingstrata are but little obstructed, and this is offset through the forcingof more of the obstructing material into the strata which by-pass water(because of the resistance due to the viscosity of the oil in the oilbearing strata), the ratio of increase of flow of oil is about four toone and this four-fold increase in production is obtained by a five-foldexpenditure of power. To obtain the same increase in oil flow by methodsheretofore used would require sixteen times the power.

In carrying out my invention, I inject into the strata, either with thewater used for flooding or by themselves, solutions acting to formprecipitates in the pores or channels of the strata. Choice ofprecipitating materials, in general, depends upon the nature of thechannels which must be obstructed and particularly on the chemicalcomposition of the sand or rock strata to be impregnated. Thus ifchannels or pores are very large, a material suspended in the Water,such as mud or clay, may suffice. If the pores to be filled are small,like those of a typical sandstone, mud or clay may fail to penetrate andmay separate from the Water at the face of the rock without effect uponthe pores of the stratum. Generally I have found that the best resultsare obtained by injecting into the strata solutions of acid salts ofmetals such as chlorids or sulfates of iron, aluminum, antimony, arsenicand like metals; salts which react with components of the rock or sandformation to form precipitates and thus to impregnate the formation. Ingeneral, salts of a strong acid combined with a metal moreelectronegative than calcium are effective. With acid salts such asthese, corrosion of pumps and piping may be prevented by the addition ofsuitable amounts of well known corrosion inhibitors. Calcium carbonateis a common constituent of the rocks which serve as oil reservoirs; thecontent of this substance often averaging about per cent of the weightof the rock. It is usually an important rock constituent available forreaction with the metallic salts which I inject into the rock strataaccording to the present invention. Magnesium carbonate occurs in lessamount as do other rocky materials of alkaline nature, such aspegmatities; these being also acted upon by salts of the above group toform precipitates. In carrying out my invention it is possible toanalyze minerals present in the strata to be obstructed, ascertainingwhat chemical bodies are available, so that known reactions may bebrought about to effect obstruction with its resulting benefits.

In some cases, by analyzing the various strata through which the inputwell passes, it has been found that the looser strata which first causebypassing of water contain compounds which are not contained in thestrata which deliver oil to the production well. In this event, achemical compound may be injected which will plug off the by-passingstratum without materially affecting the oil bearing stratum. Forexample, analysis of rock cores from the input well may show that theformation consists of fine grained ferruginous sandstone, substantiallyfree from material other than silica and iron oxid, alternating withstrata of coarse calcareous sandstone. The calcareous sandstone beingthe coarser, it will be the first to deliver its oil to the productionwell and thereafter such a stratum will allow passage of water withoutexpulsion of any substantial quantity of oil. To obstruct the calcareoussandstone without affecting the ferruginous sandstone, a quantity offerric chlorid or ferrous sulfate is added to the water introduced inthe proportion of about one pound of the salt to gallons of water. Thisaddition to the flowing water may be continued until the desiredreduction in flow of water is accomplished. The pressure upon the supplyof water may then be increased, increasing the oil production aspreviously described.

Instead of adding an impregnating agent to the flow of water introduced,I may force into the stratum a concentrated solution of a metallic salt,such, for example, as antimony trichlorid, which reacts with the waterto form an insoluble precipitate in the strata such as antimonyoxychlorid. In so doing, the concentrated reagent may be forced down thetubing preceded by a sliding wooden plug to prevent prematureprecipitation, and in quantity suflicient to impregnate the more porousstrata, but not enough to force an undue amount of the metallic solutioninto the less porous oil bearing strata. If desired the well may becleared of water prior to injection of the reagent, the plug not beingused in such case. Or, I may alternately inject two solutions which aremutually precipitable, cleaning out the well between the injections ofthe two solutions so as to avoid precipitation in the well itself andconsequent obstruction. For example, there may be successive injectionof ferrous sulfate solution and a solution of an alkali, such as causticsoda or sodium carbonate. As other examples of mutually precipitantsolutions may be mentioned those of iron or aluminum chlorid and ammoniaor a fixed alkali; calcium chlorid and sodium carbonate; magnesiumsulfate or chlorid and an alkali, etc. Or the precipitation of a ferroussalt may be accomplished with an oxidizing solution, such as watercontaining dissolved air with or without dissolved alkali. Thecharacteristics of the formation often determine the solutions to beused. I may adopt the technique well known to operators ofwater-purification plants, in forming coagulated precipitates in hardwater strata; adjusting conditions to those suitable for the particularstratum.

It is sometimes desirable to partially or completely remove aprecipitate in the strata near an input well, as a method of correctinga condition brought about by too much obstruction. For this reason Iprefer to utilize reactions resulting in precipitates which may bereadily removed. For example, ferric or aluminum hydroxid obstructionsmay be removed by the injection of mineral acid, or of acid salts likeferric chlorid or aluminum chlorid.

In practice, an input well serves to flood a considerable territoryextending radially from the well and production wells are advantageouslylocated at various points surrounding an input well. A single input wellmay serve for injection of impregnating material to prevent by-passingof water into the surrounding production wells.

In a specific example of my process applied to a water-floodingoperation, there were five wells arranged in a five-spot pattern: fourproduction wells and a water input well in the center. The fourproduction wells produced a total of 12 barrels of oil per day. In orderto obtain this production it was necessary to pump 150 barrels of waterper day into the input well. The wateroil ratio was thus 12.5 1.According to the invention the water input well was treated with a verythin mud containing about 2 pounds of silty mud per barrel of water,injected into the well under substantial pressure. This treatment forcontinued for 5 days, during which time the water input continuallydecreased until only 25 barrels of water per day were required, the samepressure being applied on the input well. The oil production continuedunchanged. Thus the water-oil ratio was reduced to approximately. 2:1.It is evident that during the treating process the very fine mud hadgone mostly into water bearing strata, and that the mud which went intothe oil bearing stratum decreased the flow to only a negligible extent.After the five day treatment with the mud slurry water was again used onthe input well with a continuation of the beneficial results.

What I claim is:

1. In a water flooding process wherein water is injected into porousstrata of various permeabilities surrounding an input well and water andoil are removed from a production well, the process which comprisesinjecting into the said input well in solution at least one substancewhich reacts with at least one component of the porous strata to form aplugging precipitate partially obstructing the pores thereof in theportions of the strata adjacent the input well, and resuming injectionof water into the input well.

2. In a water flooding process wherein water is injected into porousstrata of various permeabilities surrounding an input well and Water andoil are removed from a production well, the process which comprisesinjecting into the said input well a solution of a substance adapted toform a precipitate partially obstructing the several porous strataadjacent the input well, said substance being an acid salt of a metalselected from the class consisting of iron, aluminum, arsenic, antimonyand tin, and resuming injection of water into the input well.

3. In a water flooding process wherein water is injected under pressureinto porous strata of different permeabilities surrounding an input welland Water and oil are removed from a production well, the process whichcomprises injecting into said input well successively two liquidscontaining substances adapted to react together to form a precipitatepartially but not completely obstructing the pores of the variousdifferently permeable strata adjacent the input well, and then resuminginjection of water.

4. In a water flooding process wherein water is injected into porousstrata of various permeabilities surrounding an input well and water andoil are removed from a production well, the process which comprisesinjecting into the said input well a solution, capable of penetratingfar into porous rock, of a substance adapted to form adislodgment-resisting precipitate within the pores of the stratapartially obstructing the sev eral porous strata adjacent the inputwell, and then resuming injection of water into the input Well.

5. A process for recovering oil from porous strata in regions havingporous strata of different permeabilities, which comprises establishingand maintaining a water input well down which a drive liquid is forcedunder pressure into surrounding strata, establishing and maintaining anoil output well spaced from the input well and from which oil and driveliquid are withdrawn, and injecting into the input well and theadjoining strata a thin, temporarily fluid, porepenetrating sealingmaterial, which material in the course of time produces in the poresthereof a dislodgment-resisting seal, the amount of material injectedbeing limited to cause only a partial obstruction of the several strataadjacent the input well, and resuming injection of the drive liquid.

6. The method of claim 3 wherein the two liquids are solutions ofcalcium chloride and sodium carbonate, respectively.

HARVEY T. KENNEDY.

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